Damping device for rotary offset press

ABSTRACT

A damping device for a rotary offset printing machine comprising a trough of dampening fluid in which is partially immersed a transfer roll having a hard hydrophilic surface. A wiping roll having a flexible surface is pressed against the transfer roll. In order to prevent a build-up of sludge at the inlet to the zone of contact between the two rolls, the wiping roll is rotated very slowly at a speed between one hundreth to one tenth of the speed of the transfer roll, the sludge entrained by the wiping roll being collected by a scraper blade or other means so as to prevent it being recycled.

Chambon [451 Jan. 15, 1974 1 1 DAMPING DEVICE FOR ROTARY OFFSET PRESS [75'] Inventor:

[73] Assignee: Societe dEtudes de Machines Specials S.A., Paris, France 221 Filed: July 12,1971

211 Appl.No.: 161,545

Louis Jean Chambon, Paris, France [30] Foreign Application Priority Data July 10, 1970 France 7025901 [52] US. Cl. 101/148, 101/350 [51] Int. Cl B411 23/02 [58] Field of Search 101/148, 349, 350

[56] References Cited UNITED STATES PATENTS 3,343,484 9/1967 Dahlgren 101/350 3,038,405 6/1962 \Vojciechowski et a1 101/148 3,587,460 6/1971 Chambon t 101/148 3.285.169 11/1966 Hnrtwig i 101/350 3,026,795 3/1962 Dietrich 101/148 Primary ExaminrRobert E. Pulfrey issistggt @qniner-William Pieprz [57] ABSTRACT A damping device for a rotary offset printing machine comprising a trough of dampening fluid in which is partially immersed a transfer r011 having a hard hydrophilic surface. A wiping r011 having a flexible surface is pressed against the transfer roll. in order to prevent a build-up of sludge at the inlet to the zone of contact between the two rolls, the wiping roll is rotated very slowly at a speed between one hundreth to one tenth of the speed of the transfer roll, the sludge entrained by the wiping roll being collected by a scraper blade or other means so as to prevent it being recycled.

4 Claims, 2 Drawing Figures DAMPING DEVICE FOR ROTARY OFFSET PRESS BACKGROUND OF THE INVENTION In rotary offset printing machines of the type to which this invention is applicable, it is necessary to apply a film of a dampening medium such as water to the printing plate or cylinder. One prior art dampening device for performing this operation comprises a dampening or transfer roll which is partially immersed in a trough of the medium. The dampening roll rotates in operation and, because it has a hydrophilic surface, takes up a film of dampening medium and transfers it to a forme roll which is in contact with the plate or cylinder. The transfer roll is also in contact with a drying roll and, during operation, all of the rolls run against one another.

As those skilled in this art will be aware, this type of device has the disadvantage that the ink and dampening medium which come into contact on the forme roller emulsify and form a sludge which is constantly recycled through the damping and inking systems so that poor prints are eventually produced.

This disadvantage is overcome in another prior art device in which the drying roll, now termed the wiping roll, is kept stationary during operation so that the sludge accumulates at the inlet to the zone of contact between the transfer and wiping rolls. The sludge is therefore prevented from returning to the system so that a print of improved quality is obtained for a given length of run compared with the device previously described.

However, it is necessary to remove the accumulated sludge at intervals and this operation is performed by manually rotating and cleaning the wiping roll.

SUMMARY OF THE INVENTION It is a general object of this invention to provide a dampening device which overcomes the disadvantages of the prior art.

It is another object of the invention to provide a dampening device in which recycling of sludge can be prevented as with a stationary wiping roll, while at the same time, a build-up of sludge requiring regular cleaning can be prevented.

It is a further object of the invention to provide a damping device in which the sludge accumulating on the surface of the wiping roll can be removed simply and automatically. p 7

Accordingly, a damping device comprises a transfer roll with a hard, hydrophilic surface, the lower part of which is immersed in a trough containing a damping medium. The transfer roll is rotated at a constant but controllable speed in contact with a forme roll, and has pressed against it a wiping roll with a flexible peripheral layer. The wiping roll is driven in the opposite direction to the transfer roll but at a very slow speed of between one hundredth and one tenth of the rotational speed of the transfer roll.

The speed at which the wiping roll is driven is so low that the roll is practically stationary with the result that the sludge is prevented from returning to the inking system. Nevertheless, the rotation of the wiping roll is such that the quantity of sludge which does accumulate on the inlet side of the zone of contact between the transfer and wiping roll is passed gradually through the said zone and forms a thin film on the surface of the wiping roll down stream of the zone. This film can easily be removed either by wiping the surface with a cloth by hand or by some means of an automatic scraper in contact with the said surface.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic vertical section through a dampening device of an offset rotary printing machine,

FIG. 2 is a sectional diagram, on a larger scale, of the contact zone between the transfer roll and the wiping roll.

DESCRIPTION OF PREFERRED EMBODIMENT The dampening device shown in FIG. 1 comprises a trough 1 containing a quantity of dampening medium for example water, which is kept to a fixed level and constantly recirculated by a filtration device, such as a pump, which is not shown in the drawing. A dampening or transfer roll 2, of which the lower part is immersed in the dampening medium contained in the trough l, is integral or fast with a horizontalshaft 3. This shaft 3 and consequently the transfer roll 2 are rotated in an anti-clockwise direction as viewed in the drawing and at a constant but adjustable speed,by a variable-speed electric motor 4, via a gear train 5.

The peripheral surface of the dampening roll 2 has a comparatively hard covering with considerable affinity for water, the covering being made for example of chromium. A wiping roll 6 is mounted so that its peripheral surface contacts that of the roll 2 in a zone 7 situated substantially in a horizontal plane passing through the axis of the shaft 3. The wiping roll 6 comprises a central core 6a, of a relatively hard material, for example steel, and a surface layer 6b of a supple material such as rubber.

The wiping roll 6 is firmly pressed against the transfer roll 2, sufficiently to ensure that the surface layer 6b is considerably compressed in the contact zone 7.

The transfer roll 2 is also pressed at a position substantially diametrically opposite the zone of contact 7 with roll 6, against a roll 8 having a supple peripheral layer and rotating at a constant speed, in a clockwise direction. In a rotary press of the offset type this roll 8 can consist either of the forme roll rotating on the plate or on the etched roll 9 of the printing machine, as shown in FIG. 1, or of a distributor roll. The forme roll 8 itself is in contact, in its upper part, with an inking roll 1 l which rotates in the anti-clockwise direction and has its periphery regularly fed with ink by an inking device of a known type and not shown in the drawing. The roll 8 is freely mounted and is controlled by the rolls 9 and 11.

Thus, the transfer roll 2, which carries on its periphery an even, thin film of water a, partly deposits this film on the surface of the form roll 8, which has previously been inked by the inking roll 11. The layer of water distributes itself in more or less equal proportions between the rolls 2 and 8, downstream of their contact zone. The forme roll 8, in its turn, deposits the mixed layer of ink and water, present on its surface, onto the plate or the etched roll 9 of the printing machine. Owing to the layering effect occurring in the zone of contact under pressure between the roll 8 and the plate or the engraved roll 9, an emulsion of water in the ink is formed and continues to adhere to the surface of the rubber layer of the forme roll 8, downstream of its zone of contact with the engraved roll 9. This emulsion is carried along by the forrne roll 8 as far as the zone of contact between this roll and the transfer roll 2, whereafter some of it is transferred to the transfer roll 2 while the remainder is once again conveyed to the plate or etched roll 9. The quantity of emulsion adhering to the roll 2 is thus passed through the body of water contained in the trough 1. Some of the emulsion is washed off the roll 2 and is filtered out during recirculation while the remainder continues to adhere to the surface of the roll 2 and is thus conveyed towards the contact zone 7 between the roll 2 and the wiping roll 6.

if, as in accordance with the prior art, the wiping roll is kept stationary, the emulsion conveyed into the contact zone 7 by the roll 2, accumulates between this roll and the wiping roll 6, thus forming a mass of sludge indicated at e in FIGS. 1 and 2.

To remove the sludge formed here by the emulsion, the invention provides for the wiping roll 6 to be rotated at a very low speed in comparison with that of the roll 2. For this purpose, the shaft 12 of the wiping roll 6 is driven by the electric motor 4, via a train of reduction gears marked as a whole by the reference number 13.

The speed reduction selected for the gear tain 13 is such that the rotation speed of the wiping roll 6 is between one hundredth and one tenth of that of the roll 2.

The wiping roll 6 is rotated in the opposite direction to the roll 2, i.e., clockwise in the case of FIGS. 1 and 2.

As may be seen more clearly from FIG. 2, the froth formed by the emulsion of water and ink is caused to move in a layer or film during its passage in the contact zone 7 between the rolls 2 and 6, and the sludge which results from the layering of this froth and which is indicated by e, in FIG. 2 continues to adhere to the surface of the wiping roll 6, down stream ofthe contact zone 7.

The sludge resulting from the emulsion can be collected by a doctor blade 14 in contact with the upper portion of the peripheral surface of the wiping roll 6 or alternatively by wiping over the surface of this roll with a cloth held in the hand. This ensures the efficient operation of the dampening device, owing to the fact that the sludge caused by the emulsion of the water in the ink is eliminated without difficulty.

Those skilled in the art will understand that the above description and drawings disclose an embodiment which is purely illustrative, and that modifications may be made to the dampening device within the spirit and scope of the invention. Thus, for example, it would be possible for the roll 6 to be driven by a separate motor, or to rotate intermittently while achieving the same end result.

What is claimed is:

1. In a rotary press of the offset type having a rotating inking roll, a trough for a dampening liquid, a rotating transfer roll having a hydrophilic surface, part of said surface being disposed in said trough to pick up said dampening liquid from said trough as the transfer roll rotates, a third roll with a flexible peripheral layer in rolling contact with said inking roll and said transfer roll, and a wiping roll having a flexible peripheral layer pressed firmly against the transfer roll so as to compress said flexible peripheral layer of the wiping roll in the zone of contact with the transfer roll, means for rotating said transfer roll in a direction to engage said wiping roll after picking up dampening liquid from said trough and before engaging said third roll, the improvement comprising means for maintaining said wiping roll almost stationary so as to collect on the inlet side of the zoneof contact between the transfer roll and the wiping roll any sludge comprising an ink-dampening liquid emulsion formed on the transfer roll while rotating said wiping roll in a direction opposite to the transfer roll at a very low speed ranging from a hundredth to a tenth of the speed of rotation of the transfer roll to remove any such collection of said sludge on to the wiping roll and thereby avoid its accumulation.

2. A dampening device in accordance with claim 1, in which said means for rotating the transfer roll and said means for rotating the wiping roll comprise a single electric motor, a first gear train by means of which the transfer roll is driven by the said motor in a selected first direction, and a second reduction gear train by which the wiping roll is driven from the said motor in a second direction opposite to the aforementioned first direction of rotation, and at a speed of between one hundredth and one tenth of the speed of rotation of the transfer roll.

3. A device in accordance with claim 1, further comprising means for cleaning the wiping roll.

4. A device in accordance with claim 3, said cleaning means including a scraper contacting the peripheral surface of the wiping roll. 

1. In a rotary press of the offset type having a rotating inking roll, a trough for a dampening liquid, a rotating transfer roll having a hydrophilic surface, part of said surface being disposed in said trough to pick up said dampening liquid from said trough as the transfer roll rotates, a third roll with a flexible peripheral layer in rolling contact with said inking roll and said transfer roll, and a wiping roll having a flexible peripheral layer pressed firmly against the transfer roll so as to compress said flexible peripheral layer of the wiping roll in the zone of contact with the transfer roll, means for rotating said transfer roll in a direction to engage said wiping roll after picking up dampening liquid from said trough and before engaging said third roll, the improvement comprising means for maintaining said wiping roll almost stationary so as to collect on the inlet side of the zone of contact between the transfer roll and the wiping roll any sludge comprising an ink-dampening liquid emulsion formed on the transfer roll while rotating said wiping roll in a direction opposite to the transfer roll at a very low speed ranging from a hundredth to a tenth of the speed of rotation of the transfer roll to remove any such collection of said sludge on to the wiping roll and thereby avoid its accumulation.
 2. A dampening device in accordance with claim 1, in which said means for rotating the transfer roll and said means for rotating the wiping roll comprisE a single electric motor, a first gear train by means of which the transfer roll is driven by the said motor in a selected first direction, and a second reduction gear train by which the wiping roll is driven from the said motor in a second direction opposite to the aforementioned first direction of rotation, and at a speed of between one hundredth and one tenth of the speed of rotation of the transfer roll.
 3. A device in accordance with claim 1, further comprising means for cleaning the wiping roll.
 4. A device in accordance with claim 3, said cleaning means including a scraper contacting the peripheral surface of the wiping roll. 